For compression of video data, a plurality of video standards has been developed. Such video standards are, for example, MPEG-2, MPEG-4 and H.264/MPEG-4 AVC. As a successor to H.264/MPEG-4 AVC, High Efficiency Video Coding (HEVC) is currently under joint development by the ISO/IEC Moving Picture Experts Group (MPEG) and ITU-T Video Coding Expert Group (VCEG).
According to HEVC, one picture is divided into largest coding units (LCUs), one or more coding units of each LCU are encoded by generating a prediction block using inter prediction or intra prediction. The difference between an original block and the prediction block is transformed to generate a transformed block, and the transformed block is quantized using a quantization parameter and one of a plurality of predetermined quantization matrices. The quantized coefficients of the quantized block are scanned by a predetermined scan type and then entropy-coded. The quantized coefficients are inversely quantized and inversely transformed to generate a residual block which is combined with the prediction block to generate reconstructed image. The reconstructed image is adaptively filtered using one or more deblocking filter to remove blocking artifacts.
But, the technique of deblocking filter described in H.264 and HEVC under development deteriorates decoding performance of a decoding apparatus because the technique is too complicated. Also, even if the deblocking filtering is applied to the block edges, the differences between the original samples and the filtered samples are still remained. To compensate the differences, sample adaptive offset (SAO) process is introduced. But, according to the current SAO process, the differences between the original samples and the filtered samples increase occasionally because the optimum edge index should not be determined.
Therefore, new technique is required to reduce the complexity of the post-processing and to improve the performance of the post-processing.